FETS Ion Source Diagnostics: The Pepperpot Simon Jolly Imperial College UKNF Meeting, 03/05/06

Ion Source Emittance Simulations of FETS LEBT require correlated X & Y emittance data and space charge compensation data. Current measurements only give x-x’ and y-y’ emittance measurements, with no x-y correlation. Requirement for correlated emittance data and information on space charge compensation… Pepperpot: reduce granularity to gain correlation …  03/05/06 Simon Jolly, Imperial College

Pepperpot Principle Beam segmented by tungsten screen. Drift length of ~12mm allows beamlets to expand. Beamlets produce image on phosphor screen. Copper block prevents beamlets from overlapping. CCD camera records image of light spots. Phosphor screen Copper block Fast CCD Camera H- Ion Beam Tungsten screen H- Beamlets 03/05/06 Simon Jolly, Imperial College

Purpose of Pepperpot Current measurements only give X-X’ and Y-Y’ emittance measurements, with no X-Y correlation. Pepperpot system reduces granularity of emittance measurement to give correlated measurements: Arrangement of spots gives (sampled) beam size: X-Y profile. Expansion and displacements of spots gives X-X’ and Y-Y’ emittance (and also X’-Y’ should we need it). Sampling at several positions gives space charge estimate (compare to GPT simulation). 03/05/06 Simon Jolly, Imperial College

Pepperpot Components Tungsten grid (25 x 25 holes, 100m diam, 3mm spacing). Copper block allows beamlets to expand. Phosphor screen images beamlets. Light from phosphor recorded by fast CCD camera (500ns shutter). Lens system mounted on camera improves resolution. Light path enclosed in light tight bellows. Whole system mounted on moving stage to allow longitudinal beam sampling (but camera-to-phosphor distance fixed). 03/05/06 Simon Jolly, Imperial College

FETS Pepperpot System (PJS) Complete Pepperpot assembly: Screen assembly produces beamlets and image on phosphor. Camera (+ lens) records phosphor image. Support structure “stolen” from previous system at RAL. Longitudinal motion from screw thread. 03/05/06 Simon Jolly, Imperial College

FETS Pepperpot System (2) Pepperpot screen assembly: Tungsten screen (100m holes with 3mm spacing). 10mm thick copper block. Phosphor screen (P46 or P47 phosphor on glass substrate). Aluminium mounting block. 03/05/06 Simon Jolly, Imperial College

FETS Pepperpot System (3) Pepperpot camera assembly: PCO 2000 camera with 2048 x 2048 pixel, 15.3 x 15.6 mm CCD. Firewire connection to PC. 105 mm Micro-Nikkor macro lens (not shown). Whole structure mounted on moving stage: 3-arm spider improves sability. 03/05/06 Simon Jolly, Imperial College

Complete Pepperpot System Assembled Pepperpot System at IC Pepperpot block + mount Bellows Camera + lens Vacuum flange 03/05/06 Simon Jolly, Imperial College

Pepperpot Calibration Images Calibration Images from setup at IC 03/05/06 Simon Jolly, Imperial College

Pepperpot Data Calibration Image Ion Source Background 03/05/06 Simon Jolly, Imperial College

Next steps Complete calibration & analysis software in Matlab: Need prediction of actual hole location before we can calculate emittance. Alignment comes from “ruler” image: correlate to hole position using test data. Fix vacuum leaks (new seals/bellows). Make improved hole size measurements on tungsten screen. Improved tungsten screen with 50m holes. Take some real data… 03/05/06 Simon Jolly, Imperial College